Ultrafast electron diffraction optimized for studying structural dynamics in thin films and monolayers

Abstract

A compact electron source specifically designed for time-resolved diffraction studies of free-standing thin films and monolayers is presented here. The sensitivity to thin samples is achieved by extending the established technique of ultrafast electron diffraction to the “medium” energy regime (1–10 kV). An extremely compact design, in combination with low bunch charges, allows for high quality diffraction in a lensless geometry. The measured and simulated characteristics of the experimental system reveal sub-picosecond temporal resolution, while demonstrating the ability to produce high quality diffraction patterns from atomically thin samples.

Photoinduced Structural Dynamics of Molecular Systems Mapped by Time-Resolved X-ray Methods

“…Ultrafast electron-based techniques have made strident progress thanks in particular to the huge contributions of the late Ahmed Zewail 56,58,60 and of others. 365,366 However, ultrafast 1D or 2D IR spectroscopies 367,368 along with ultrafast Raman spectroscopy, offer many features that are found in X-ray based techniques but with the advantage of being lab-based and therefore requiring less technical investment. Processes such as solvent heating (shown in Figure 15 for the X-ray case) are routinely investigated with IR methods, correlations between various chromophores within a complex system can be detected by 2D IR spectroscopy, provided couplings exist between them.…”

Optical fiber-based photocathode

“…Finally, we embedded our fiber-based photocathode inside a bulk cathode structure which is optimized for use in high extraction fields as typically employed in compact DC guns (typically in the keV to hundreds of keV regimes [7][8][9]22,28 ) or radio-frequency (RF) guns ranging into MeV energies. 27 The feasibility of this arrangement was tested in a DC electron gun at an acceleration field of 7 MV/m, and beam energy of 70 kV (see the supplementary material for details).…”

Исследование Твердотельной Структурной Динамики С Помощью Сверхбыстрой Электронной Дифракции И Микроскопии

“…В рамках выполненного эксперимента нулевая точка отсчёта определяется пересечением двух прямых, одна из которых соответствует плато, а другая -переднему фронту изменения сигнала (рис. 3, c) [29]. Найденное таким образом положение нулевой точки оказалось размытым на величину около 10 ps, что близко к численной оценке длительности электронного импульса, равной 7.5 ps [28].…”